Part of the reason the project — named the “Kola Superdeep Borehole” — wasn’t widely known at the time was because the former Soviet Union initially supervised the operation (located within Russia’s Kola Peninsula), and some details were likely kept under wraps.
Records show that drilling began in May 1970, and continued sporadically over nearly a quarter-century. By the time the project was called off, drill teams had reached a depth of over seven miles — which is actually deeper than the lowest point of the Mariana, making it officially the deepest hole ever measured on Earth. That record still stands today
So… what exactly did they find down there?
No ancient subterranean beasts slithered up from the depths to attack the drilling team (at least as far as we know), but scientists did make some bizarre discoveries. To begin with, they found two dozen different species of fossilized microorganisms over four miles down, estimated to be around 2.5 billion years old.
Weirdly enough, they also found the deepest traces of water ever reached — literally squeezed out of crystallized hydrogen and oxygen in the rocks below (drilling released some of these gases, which caused the mud extracted from the hole to boil).
As they drilled beyond that, teams began to encounter extreme temperatures, reaching over 350 degrees by seven miles down. The heat was so intense, in fact, that the drill bit would eventually no longer function. The project was halted in 1992, though the facility wasn’t officially shut down until 2006.
Considering the Earth’s crust in the Pola Peninsula is estimated to be over three times deeper than the drill finally reached, we can only theorize what could have been found had they been able to continue further…